In addition to chemical vapor deposition methods or physical vapor deposition methods, atomic layer deposition has recently been suggested as a method of forming thin films of semiconductor devices. In atomic layer deposition, thin films are formed on a wafer by alternately supplying at least two kinds of source gases required to obtain desired thin films into a chamber in which thin films are deposited. Atomic layer deposition is useful in forming high quality thin films and integrating semiconductor devices due to the ease of thickness control.
Meanwhile, in forming capacitors of semiconductor memory devices, more stabilized capacitance of capacitors is required as the size of semiconductor devices is reduced. However, obtaining more stabilized capacitance by reducing the thickness of dielectric layers or increasing the area of capacitors is becoming increasingly difficult. Therefore, research on using a dielectric layer having a high dielectric constant (k) to obtain stabilized capacitance is currently being conducted including research on replacing conventional dielectric layers formed of silicon oxide (dielectric constant 3.9), silicon nitride layer (dielectric constant 7.2), silicon nitride in a multi-layer structure and silicon oxide (ONO, dielectric constant 7.9˜7.2) with other materials having high dielectric constants.
Examples of materials that can be used to form high-k dielectric layers to replace the above conventional dielectric layers include tantalum oxide (dielectric constant 20˜60), hafnium oxide (dielectric constant 20), titanium oxide (dielectric constant 40), aluminum oxide (dielectric constant 10), lanthanum oxide (dielectric constant 20), etc. Also, ferroelectric multi-layer structures such as PZT (barium strontium titanate), BST (Lead zirconate titanate) and STO (strontium titanate oxide) can be used as dielectric layers.
However, precursors of the above-described materials that can be used to form high-k dielectric layers generally have relatively large molecular weights and exist in a solid state at room temperature. Thus, it is difficult to deposit the above-described materials when forming dielectric layers of semiconductor devices.
FIG. 1 is a flowchart illustrating a conventional atomic layer deposition method of forming dielectric layers.
Referring to FIG. 1, firstly a wafer is arranged in a chamber, and a first source gas is supplied (S10). Next, the first source gas is purged (S20). Subsequently, a second source gas is supplied (S30) and purged (S40). Then, S10 through S40 are repeated (S50) to deposit a thin layer such as a dielectric layer having a desired thickness on the wafer.
In the conventional atomic layer deposition method as illustrated in FIG. 1, a first source gas having a relatively large molecular weight and existing in a solid state at room temperature is used and thus the precursor of the first source gas is used with an organic solvent added thereto for volatility and stability. However, when the precursors are vaporized in a vaporizer of the atomic layer deposition apparatus, the precursors are decomposed to metal compounds or organic materials to form precipitable intermediates or leave unvaporized residues in the vaporizer. As a result, a nozzle of the vaporizer can be blocked or the operating capability of the vaporizer can deteriorate.